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Analog Devices Inc. LTC3851AIMSE#PBF
- Part No.:
- LTC3851AIMSE#PBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- DC DC Switching Controllers
- Package:
- 16-TFSOP (0.118", 3.00mm Width) Exposed Pad
- Datasheet:
-
LTC3851AIMSE#PBF.pdf
- Description:
- IC REG CTRLR BUCK 16MSOP
- Quantity:
- Payment:
- Shipping:
Inventory:856
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Product details
Overview
LTC3851AIMSE#PBF from Analog Devices (formerly Linear Technology) is a high-performance synchronous step-down switching regulator controller driving dual N-channel MOSFETs in a constant-frequency current-mode architecture. It operates from 4V to 38V input, delivers 0.8V–5.5V output with ±1% accuracy, supports phase-lockable 250kHz–750kHz switching, and enables Burst Mode™ for ultra-low-light-load efficiency-used in telecom power supplies requiring tight regulation and thermal robustness.
For engineers reviewing the LTC3851AIMSE#PBF datasheet, LTC3851AIMSE#PBF pinout, LTC3851AIMSE#PBF application, or LTC3851AIMSE#PBF equivalent, key selection criteria include its 16-lead MSOP package with exposed thermal pad, OPTI-LOOP® compensation for wide output capacitor/ESR tolerance, adjustable current foldback, and precise 0.8V reference compatible with distributed DC systems.
Technical Context
The LTC3851AIMSE#PBF implements a constant-frequency current-mode control loop where peak inductor current is set by the ITH voltage, and output voltage is regulated via error amplifier comparison of VFB against a 0.8V reference. Its transconductance amplifier (2 mmho, 3 MHz GBW) drives the current comparator with slope compensation to prevent subharmonic oscillation at duty cycles >50%.
It integrates a 5V internal LDO (INTVCC) powering gate drivers and logic, supports RSENSE or DCR current sensing, and features programmable light-load operation-Burst Mode™ (via resistor on MODE/PLLIN), pulse-skipping, or forced continuous conduction-each with distinct ripple, efficiency, and EMI trade-offs.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 4V to 38V - supports wide industrial and telecom input rails without pre-regulation. |
| Output Voltage Accuracy | ±1% over temperature - ensures stable rail generation for sensitive analog/digital loads. |
| Switching Frequency | 250kHz to 750kHz, phase-lockable - balances efficiency vs. magnetics size; PLL sync enables noise-sensitive system clock alignment. |
| Reference Voltage | 0.8V ±1% - standard for modern low-voltage CPUs/FPGAs; enables precise scaling with external resistor dividers. |
| Shutdown Quiescent Current | 20µA - minimizes standby power loss in battery-backed or always-on systems. |
| Current Sense Threshold Options | 30mV / 50mV / 75mV (via ILIM pin) - allows flexible trade-off between current limit precision and sense resistor power loss. |
| Thermal Performance | θJA = 40°C/W (MSOP) - requires exposed pad soldering for reliable 125°C junction operation under full load. |
Pinout & Package
Package: 16-lead plastic MSOP (MSE) with exposed thermal pad (Pin 17 = GND), rated for –40°C to 125°C operating junction temperature.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| MODE/PLLIN (Pin 15) | Mode selection & external clock input | Selects Burst Mode™, pulse-skipping, or forced CCM; accepts external sync clock up to 750kHz for EMI reduction. |
| FREQ/PLLFLTR (Pin 16) | PLL loop filter / frequency programming node | Connects RC network to set oscillator frequency or serve as PLL low-pass filter when synchronized. |
| RUN (Pin 1) | Enable/disable control | 1.22V threshold with 120mV hysteresis; internal 2µA pull-up enables simple RC soft-start sequencing. |
| TK/SS (Pin 2) | Soft-start/tracking ramp input | 1µA internal current charges external capacitor for controlled VOUT ramp; supports ratiometric or coincident tracking of master supply. |
| ITH (Pin 3) | Error amplifier output & current threshold | Directly sets peak inductor current; used for loop compensation and current foldback during short-circuit events. |
| VFB (Pin 4) | Feedback input | Compares output divider voltage to 0.8V reference; high-impedance (–50nA) input minimizes divider loading error. |
| SENSE+ / SENSE– (Pins 5–6) | Differential current sense inputs | Accepts Kelvin-connected RSENSE or DCR network; ±2µA input bias enables accurate low-value sensing. |
| ILIM (Pin 7) | Tri-level current limit select | GND/FLOAT/INTVCC selects 30/50/75mV max sense threshold - configures current limit without changing sense resistor. |
| GND (Pins 8, 17) | Signal & thermal ground | Exposed pad (Pin 17) must be soldered to PCB ground plane for thermal integrity and low-noise small-signal referencing. |
| BG (Pin 9) | Bottom gate driver output | Drives low-side N-MOSFET gate from GND to INTVCC; 1.1Ω pull-down ensures fast turn-off and shoot-through prevention. |
| INTVCC (Pin 10) | Internal 5V regulator output | Supplies gate drivers and core logic; requires ≥2.2µF low-ESR ceramic/tantalum decoupling to GND. |
| VIN (Pin 11) | Main input supply | 4V–38V input rail; decoupled externally to minimize high-frequency switching noise injection. |
| BOOST (Pin 12) | Floating bootstrap supply | Charged via external diode/capacitor; swings from ~INTVCC–0.4V to VIN+INTVCC to drive high-side gate above SW node. |
| TG (Pin 13) | Top gate driver output | Floating driver referenced to SW node; 2.2Ω pull-up/1.2Ω pull-down ensures fast, low-loss high-side MOSFET switching. |
| SW (Pin 14) | Switch node connection | Connects to inductor and high-side MOSFET source; experiences full VIN-to-GND swing with fast edges - critical for layout and EMI control. |
Key Features
| Feature | Design Value |
|---|---|
| OPTI-LOOP® Compensation | Minimizes required output capacitance and relaxes ESR constraints - simplifies design across diverse ceramic/polymer capacitor types. |
| Adjustable Output Soft-Start / Tracking | Enables controlled power-up sequencing and ratiometric startup with master supplies - prevents latch-up in multi-rail systems. |
| Output Overvoltage Protection (OVP) | Shuts off top MOSFET and turns on bottom MOSFET upon >10% VOUT overshoot - protects downstream ICs from transient damage. |
| Current Foldback Limiting | Reduces MOSFET power dissipation during output short-circuit - maintains safe thermal margin without external circuitry. |
| DCR or RSENSE Current Sensing | Supports cost-effective inductor DCR sensing or high-accuracy shunt resistors - accommodates both high-current and precision applications. |
Applications
| Telecom Power Supply | Industrial PLC Module |
|---|---|
Use Scenario: 48V intermediate bus conversion to 3.3V/5V for base station RF front-end and digital signal processors. IC Role / Device Role / Timing Role: Primary synchronous buck controller regulating isolated point-of-load rails with tight transient response and low EMI. Use Value: Phase-lockable 750kHz operation aligns switching noise away from sensitive RF bands; ±1% VOUT accuracy ensures DSP core stability. | Use Scenario: 24V factory automation input converted to 12V/5V for I/O modules, sensors, and microcontrollers. IC Role / Device Role / Timing Role: High-reliability buck controller supporting wide input range and extended temperature operation (–40°C to 125°C). Use Value: 38V max input withstands load-dump transients; current foldback protects MOSFETs during field-wiring faults. |
| Distributed DC Power System | Automotive Infotainment Head Unit |
Use Scenario: Central 28V battery bus stepped down to 1.2V/1.8V for FPGA and memory subsystems in data center rack power architecture. IC Role / Device Role / Timing Role: High-efficiency, thermally optimized controller enabling compact, fanless power delivery with minimal heatsinking. Use Value: 40°C/W θJA (MSOP) and exposed pad enable >15A operation in space-constrained modules; Burst Mode™ extends standby time. | Use Scenario: 12V vehicle battery converted to 5V USB and 3.3V MCU supply in head unit with strict automotive EMC requirements. IC Role / Device Role / Timing Role: EMI-conscious buck controller using synchronized switching and low-noise pulse-skipping mode. Use Value: MODE/PLLIN synchronization eliminates beat frequencies; low shutdown IQ (20µA) meets ISO 16750 quiescent current limits. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar synchronous buck controller applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LTC3851EMSE#PBF | Same functionality but rated for 0°C to 85°C junction temperature (E-grade); lacks extended –40°C to 125°C qualification. | Suitable only for commercial-temperature environments; not qualified for industrial or automotive ambient extremes. | Select LTC3851AIMSE#PBF for designs requiring guaranteed operation at –40°C or 125°C ambient. |
| LTC3851-1IMSE#PBF | Includes power-good (PGOOD) output; replaces adjustable current limit with fixed PGOOD assertion at VOUT ≥92% nominal. | Required where system-level power sequencing or fault reporting depends on a dedicated status signal. | Choose LTC3851-1IMSE#PBF only if PGOOD is mandatory; LTC3851AIMSE#PBF offers superior current limit flexibility via ILIM pin. |
Compared with LTC3851EMSE#PBF, the LTC3851AIMSE#PBF provides extended temperature reliability for harsh environments, while LTC3851-1IMSE#PBF trades current limit adjustability for integrated power-good signaling-making the original LTC3851AIMSE#PBF optimal for thermally demanding, flexibly configured power systems.
Availability
LTC3851AIMSE#PBF is available at Aetrix Electronics and suitable for telecom power supplies, industrial PLC modules, and distributed DC power systems requiring stable component supply, long-term lifecycle support, and guaranteed –40°C to 125°C operation.
Supply support for LTC3851AIMSE#PBF includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.
Manufacturer
Analog Devices, Inc. (ADI) is a global leader in high-performance analog, mixed-signal, and power management semiconductors, formed through the acquisition of Linear Technology in 2017.
The LTC3851A product line delivers high-efficiency, thermally robust synchronous buck controllers for demanding industrial, telecom, and automotive power conversion applications-designed for reliability under wide input ranges and extreme temperature conditions.
FAQ
What is the maximum input voltage rating for the LTC3851AIMSE#PBF?
The LTC3851AIMSE#PBF has an absolute maximum input voltage (VIN) rating of 40V, with recommended continuous operation from 4V to 38V. Exceeding 40V risks permanent damage per Absolute Maximum Ratings. The device's 38V upper limit supports common industrial and telecom intermediate bus voltages including 24V, 28V, and 48V-derived rails.
How does the ILIM pin configure current limiting on the LTC3851AIMSE#PBF?
The ILIM pin on the LTC3851AIMSE#PBF provides tri-level current limit selection: grounding sets max sense threshold to 30mV, floating sets it to 50mV, and tying to INTVCC sets it to 75mV. This directly scales the peak inductor current without changing the sense resistor value, enabling flexible trade-offs between current limit accuracy, power loss, and MOSFET SOA margins in the LTC3851AIMSE#PBF design.
Can the LTC3851AIMSE#PBF synchronize to an external clock, and what pins are involved?
Yes, the LTC3851AIMSE#PBF supports external clock synchronization via its MODE/PLLIN pin (Pin 15), which serves as the phase detector input. When an external clock (250kHz–750kHz) is applied, the internal oscillator locks to it, forcing continuous conduction mode. The FREQ/PLLFLTR pin (Pin 16) must be connected to GND through an RC network to function as the PLL loop filter during synchronization.
What thermal considerations apply to the LTC3851AIMSE#PBF in its MSOP package?
The LTC3851AIMSE#PBF in the 16-lead MSOP package has a thermal resistance θJA of 40°C/W when the exposed pad (Pin 17) is properly soldered to a PCB ground plane. To maintain ≤125°C junction temperature, board layout must provide adequate copper area and thermal vias under the pad. Derating is required above 125°C, and operation beyond TJMAX = 125°C degrades lifetime reliability of the LTC3851AIMSE#PBF.
Does the LTC3851AIMSE#PBF support output voltage tracking, and how is it implemented?
Yes, the LTC3851AIMSE#PBF supports output voltage tracking via the TK/SS pin (Pin 2). By connecting an external resistor divider from a master supply to GND at this pin, the LTC3851AIMSE#PBF regulates VFB to match the TK/SS voltage during startup-enabling ratiometric or coincident tracking. An internal 1µA current also allows simple capacitor-based soft-start ramping for controlled power-up sequencing.
LTC3851AIMSE#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 16-TFSOP (0.118", 3.00mm Width) Exposed Pad
- Packaging:
- Tube
- Product Status:
- Active
- Output Type:
- Transistor Driver
- Function:
- Step-Down
- Output Configuration:
- Positive
- Topology:
- Buck
- Number of Outputs:
- 1
- Output Phases:
- 1
- Voltage - Supply (Vcc/Vdd):
- 4V ~ 38V
- Frequency - Switching:
- 235kHz ~ 750kHz
- Duty Cycle (Max):
- 99%
- Synchronous Rectifier:
- Yes
- Clock Sync:
- No
- Serial Interfaces:
- -
- Control Features:
- Current Limit, Enable, Frequency Control, Soft Start, Tracking
- Operating Temperature:
- -40°C ~ 125°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 16-MSOP-EP
LTC3851AIMSE#PBF FAQ
1.How can I place an order for LTC3851AIMSE#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LTC3851AIMSE#PBF on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.
2.Are the price and stock information for LTC3851AIMSE#PBF reliable?
The price and inventory of LTC3851AIMSE#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LTC3851AIMSE#PBF is usually 5 days.
3.What payment methods are accepted for LTC3851AIMSE#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LTC3851AIMSE#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LTC3851AIMSE#PBF?
LTC3851AIMSE#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LTC3851AIMSE#PBF order is processed, you will receive an email with the shipment details and tracking number.
Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.
5.How can I obtain technical support or documentation for LTC3851AIMSE#PBF?
For technical support, including LTC3851AIMSE#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LTC3851AIMSE#PBF requirements.
6.How does Aetrix verify that LTC3851AIMSE#PBF is sourced from the original manufacturer or authorized distributors?
All LTC3851AIMSE#PBF products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that LTC3851AIMSE#PBF meets industry standards.
7.What is the process for return or replacement of LTC3851AIMSE#PBF?
All LTC3851AIMSE#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LTC3851AIMSE#PBF, returns or replacements are accepted under the following conditions:
1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.
2.The issue is reported within 90 days of delivery.
3.The LTC3851AIMSE#PBF part is unused and in its original packaging.
Return procedure for LTC3851AIMSE#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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